QUESTION: I have often heard questions about assessing the environmental impact of A versus B answered with a common metric in order to compare apples to apples. The metrics are usually in quantity of carbon released or in dollars. Is there a more sophisticated environmental impact index out there that encompasses multiple metrics at once?Asked by Jana Watson-Capps, Longmount, Colo.

ANSWER: You pose an excellent question: while a one-metric method might comprehensively answer environmental impact questions for drying your hands or going vegetarian, using a more holistic assessment is crucial in assessing other environmental conundrums. The “ecological footprint analysis,” one of the most user-friendly and well-documented options, is a comprehensive measure of human impact on ecosystems and resources and incorporates many more factors than the more commonly calculated “carbon footprint” metric. The ecological footprint analysis has its basis in the notion of carrying capacity, or the maximum population size that an environment’s natural resources can sustain. Therefore, the ecological footprint for any given activity, project or population is expressed as the area of land and water that would theoretically be required to sustain it indefinitely.

So how do you calculate an ecological footprint? First, a survey compiles answers to questions about daily activities, such as, “how much meat do you eat every week?” and, “do you drive a car or take public transportation?” Next, the program sorts the impacts of that population into four categories: Carbon, Food, Housing, and Goods and Services. The computer then calculates average usage in each category, and returns the land area and water required to provide the natural resources for that level of consumption.

Ecological footprint analysis can be an effective way to compare competing projects, for example. But it can also help us see deeper truths about human activities at a global scale. The aptly named Global Footprint Network estimated in 2006 that humanity’s total ecological footprint was 1.4 planet Earths. In other words, we are using Earth’s resources 1.4 times faster than the Earth can renew them, drawing down the planet’s natural capital like so many credit-bingeing consumers. Take a look at the world map below depicting individual countries’ per capita ecological footprint. If some countries look bloated, the problem is more widespread than too many potato chips, and the ultimate result will be more devastating than any credit crunch.

World Consumption Cartogram (Image courtesy of pthbb.org)

Despite complex calculation metrics, ecological footprint analysis produces very accessible results, and there are online shortcuts you can use. For starters, you can take this quick, informative quiz to assess your personal impact on the globe. For me, an environmentally conscious American, the quiz estimates that it would take more than five planet Earths to sustain humanity if everyone lived a lifestyle like mine! Fortunately for those of us on the high ends of the spectrum, the website also has great practical tips for reducing your personal footprint.

Approaches like ecological footprint analysis are essential in our times of intense environmental debate. Rosamond Naylor, a Stanford Ph.D, professor and director of the Stanford Program on Food Security and the Environment, perhaps explains it best: “If you’re really thinking about choices of what kind of food we are going to grow,” says Naylor, “or what kind of transportation we want to use, or what kind of electric utilities we want to design, you’re going to have to compare the full range of costs and benefits associated with that.” Only then, she says, can we make smart decisions about sustaining the planet. “Do you care more about the carbon, or do you care more about the land?,” Naylor asks. Well, both, of course. But knowing the overall footprint can help us better understand the tradeoffs between the different impacts of our actions.